DE102019211215A1 - MR measurement with an MR local coil applied to an object in a relatively movable manner - Google Patents

Abstract

A method (S0.1-S0.4, S1-S7) is used to carry out an MR measurement on an object (P) by means of at least one MR local coil (2) applied to the object (P) in a relatively movable manner, in which an MR -Scan is carried out by means of the at least one MR local coil on the object (S2-S7), a size of a movement (<ΔV>) of the at least one MR local coil (2) being determined during the MR scan (S2-S7) is (S3-S4) and, if the size of the movement (<ΔV>) reaches or exceeds a specified tolerance (<T>) (S5), at least one action is triggered (S6). An MR system (MRS) has a data processing device (3c, 5b, 8) which is set up to allow the method (S0.1-S0.4, S1-S7) to run. The invention is particularly applicable to performing MR scans by means of an inflexible body trunk or torso coil, for example in the form of a chest, abdomen, pelvis and / or back coil, with a BO field of at least seven Tesla.

Description

The invention relates to a method for performing an MR measurement on an object by means of at least one inflexible MR local coil applied relatively movably to the object, in which an MR scan is performed on the object by means of the at least one MR local coil. The invention also relates to an MR system having at least one MR local coil, at least one position determination device for determining a position of the at least one MR local coil, and a data processing device, the data processing device being set up to allow the method to run. The invention also relates to a computer program product, comprising commands which, when executed, cause a data processing device to execute the method. The invention also relates to a computer-readable storage medium, comprising instructions which, when executed by a data processing device, cause the data processing device to execute the method. The invention is particularly applicable to performing MR scans by means of an inflexible body trunk or torso coil, for example in the form of a chest, abdomen, pelvis and / or back coil, with a BO field of at least seven Tesla.

Combined RF transmitter / receiver coils (also known as antennas) are used to excite signals in MR scanners with ultra-high magnetic fields of at least seven Tesla and frequencies of more than 300 MHz. It is known to use stationary local transmitter / receiver coils which offer particularly good transmission efficiency for a particular body region to be examined (e.g. head, knee, hand, foot, etc.). In order to homogenize the transmission field, several transmit / receive coils can be controlled in parallel with adjustable phase and amplitude. This is also known as pTX (“Parallel Transmit”) technology. The RF pulse shapes used generate a complex sequence of heat input into the patient's tissue. In order to be able to calculate the resulting SAR ("Specific Absorption Rate") e.g. by means of HF simulations using various coil / body models (see also below), precise knowledge of the local field properties is required. In some parts of the body, this is possible due to a stationary and rigid transmitter resonator, e.g. when using a head or knee coil.

In the area of the body trunk, for example, a pre-calculation is problematic, since the local coil should adapt to the patient's geometry as much as possible, e.g. an abdomen, heart or liver coil.

In the case of typical field strengths of the B0 field in the range of 1.5 Tesla and 3 Tesla, flexible surface coils, which cling variably to an area of the body, can be used to some extent with rigid coil elements within the patient bed. Since the transmission function is taken over by the HF body coil at these field strengths, the shape and position of the flexible coils have no influence on the SAR (“Specific Absorption Rate”) calculations, since the reception elements are detuned during transmission.

In contrast to this, the position and amplitude of areas with high SAR (so-called "SAR hotspots") can change noticeably with combined transmitter / receiver coils for field strengths of seven Tesla or more as a result of patient and / or coil movement. This already applies to single-channel coils, but is even more pronounced for multi-channel pTX coils.

It is known to recognize when critical SAR values are exceeded in a patient's body during an MR measurement by evaluating a change over time in a reflected radiation. However, this method is quite imprecise and unreliable.

It is also known to arrange transmitting / receiving coils on an MR local coil with rigid or partially rigid areas. Patient data (including a patient's anatomy (e.g. height and body circumference of the patient), age, weight, gender, etc.) and the patient's position relative to the MR local coil then remain as variable variables for creating a body / coil model.

To calculate the SAR in the patient, RF simulations are now carried out, the position and amplitude of critical SAR hotspots for various body models (e.g. provided as a "virtual family" from ITIS), body weights and positions of the MR local coil on the patient determine. Taking into account the remaining uncertainties such as the finite number of body models and / or a possible change in position of the patient in relation to the MR local coil during the measurement, an SAR safety factor in the form of a so-called "K-factor" is determined, which is a scale factor between the requested service and represents 10 grams of local SAR ("localSAR") in patient tissue. The transmission power radiated in during an MR measurement or an MR scan is then modified with the K factor (typically according to LocalSAR = K * transmission power) in order to keep the local SAR below a critical value. The disadvantage is that “worst case” assumptions about the movement of the patient against the local coil must be included in the calculation of the K-factor in order to ensure patient safety to guarantee. This reduces the usable SAR power of the MR local coil and thus important parameters such as a number of possible slices in a measurement and / or a measurement duration.

For the parallel operation of several transmit / receive coils ("pTX operation") of the MR local coil, an analogous procedure is known, which is based on the principle of so-called "Virtual Observation Points" (VOPs). The determination of a VOP data set (“VOP matrix”) for the pTX operation also requires the knowledge and prediction of couplings and reflections of the individual transmit / receive coils, also for the cases of undesired relative movements between the MR local coil and various large / bulky patients. Within this parameter range (which takes into account an increase in the local SAR hotspot due to coupling of the transmitter elements and position variation of the body models in the simulated patient collective), the worst case SAR is also determined and added to the VOP matrix as a safety factor. There are similar restrictions for the usable coil performance as in single-channel operation with a K-factor.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and, in particular, to provide a more reliable way of detecting that a critical SAR value in a patient is exceeded, caused by patient movement, while maintaining a high SAR output.

This object is achieved according to the features of the independent claims. Preferred embodiments can be inferred in particular from the dependent claims.

The object is achieved by a method for performing an MR measurement on an object by means of at least one MR local coil applied to the object in a relatively movable manner, in which an MR scan is performed on the object by means of the at least one MR local coil, during which MR scans determine a size of a movement of the at least one MR local coil and, if the size of the movement reaches or exceeds a predetermined tolerance, at least one action is triggered.

This method has the advantage that a patient's movement can be determined more reliably and more precisely than before, since a position of the MR local coil is physically determined or measured. This makes use of the fact that a movement or change in position of the MR local coil provides a robust indication of a relative movement between the MR local coil and the patient: if the patient moves only slightly, he also generates only a small movement of the MR local coil. The possible relative movement between the local coil and the patient is then also very likely to be small. If, on the other hand, the patient moves heavily, a strong relative movement and strong movement of the MR local coil can also occur. In the present case, the movement of the MR local coil is used as a measure or indicator for a possible relative movement between the MR local coil and the patient. The movement of the MR local coil is advantageously much easier to measure than a relative movement in which the position of the patient would also have to be measured. This applies in particular to MR local coils or coil lower parts thereof on which the patient can be supported.

With the direct determination of the movement of the MR local coil, the further advantage is achieved that for calculating the SAR safety factor (K-factor or VOP-factor) it is no longer necessary to take into account any possible or probable relative movement and the SAR safety factor then calculated reduces the SAR output less than before. The certainty that no critical SAR hotspots caused by patient movement are generated in a patient is now achieved by monitoring the movement of the MR local coil to ensure that it remains within a predetermined tolerance. This, in turn, is associated with a better usable SAR performance or power of the MR local coil, which in turn results in a shorter measurement time and / or a higher number of slices.

Another advantage is that flexible use of MR local coils in the body trunk area is made easier. For example, the use of the same MR local coils in more than one scan region is made easier, e.g. for measuring the heart region and prostate. The position-dependent VOP parameter sets required for this can be expanded from one scan area to several scan areas (or the entire trunk of the body).

This method can also advantageously be carried out without interfering with or changing the MR sequences.

There is also the advantage that the method can be retrofitted with little effort.

The MR measurement can also be referred to as an MR scan. The MR measurement can have one or more MR sequences carried out one after the other. An MR sequence can be designed as a spin echo train, which can also be referred to as a TSE (“Turbo Spin Echo”) method.

The object can be a human, an animal, or another living object.

The fact that the MR local coil is applied to the object in a relatively movable manner includes in particular that it makes contact with the object and is itself movable, in particular is at least partially movable with a movement of the object. This can be achieved, for example, by attaching or fastening the MR local coil to the object, e.g. using straps, Velcro strips, etc. Alternatively or additionally, the MR local coil can be movably attached to a patient table, e.g. using belts, Velcro strips, etc.

A movement of the MR local coil can in particular be understood to mean a change in position, specifically in one, two or three directions or spatial dimensions.

A tolerance or a tolerance range of the movement is understood to mean, in particular, a deviation from an immovable position that does not yet require or result in any action. The tolerance can also be understood as a still permissible deviation from the stationary position, at which a critical SAR or SAR hotspot is not yet generated in a patient.

It is an embodiment that the MR local coil has at least one transmit / receive antenna or coil and the at least one transmit / receive antenna is arranged on a rigid or rigid area or part of the MR local coil. In particular, the MR local coil can have at least one rigid or rigid region or part on which a plurality of transmit / receive antennas are positioned in a stationary arrangement with respect to one another. The MR local coil can have a plurality of such rigid regions which can be arranged in a flexible manner relative to one another. For this purpose, the rigid areas can be connected to one another via belts, straps, joints, etc. For example, the MR local coil can have an upper part to be attached anteriorly and a lower part to be attached posteriorly. The MR local coil is in particular not designed as a flexible mat. The MR local coil can also be referred to as an “inflexible” MR local coil in the above sense.

In one embodiment, to determine the movement, a “current” position of the at least one MR local coil is measured and its difference from a reference position is determined. This difference or position difference can be determined or calculated for one direction or separately for several directions. The current position and the reference position can have one or more components. If there are n components, they can also be represented by an n-tuple.

ausgedrückt werden, wobei sowohl ΔV_x als auch ΔV_y innerhalb ihrer Toleranzen T_x bzw. T_y bleiben müssen. For example, the current position <Vakt> can have two components Vakt_x and Vakt_y, which indicate a current position in an x-direction or y-direction. Similarly, the reference position <Vref> can be expressed by Vref_x and Vref_y. The movement <ΔV> can in a variant as $$〈\Delta \text{V}〉=\left|〈\text{Vakt}〉-〈\text{Vref}〉\right|\text{or}〈\begin{array}{c}\Delta \text{V\_x}\\ \Delta \text{V\_y}\end{array}〉=〈\begin{array}{c}\left|Vakt\text{\_}x-Vref\text{\_}x\right|\\ \left|Vakt\text{\_}y-Vref\text{\_}y\right|\end{array}〉$$

be expressed, both ΔV_x and ΔV_y must remain within their tolerances T_x and T_y.

mit T einem skalaren Wert angesetzt werden.However, as a condition for triggering an action, for example $$\Delta \text{V}={\left[{\left(\text{Vakt\_x}-\text{Vref\_x}\right)}^2+{\left(\text{Vakt\_x}-\text{Vref\_x}\right)}^2\right]}^{1/2}\ge \text{T}$$

with T a scalar value.

If several sensors, in particular proximity sensors, are used to determine the position, in a further development, as a condition for triggering an action, the position difference or movement determined via each individual sensor can be compared separately with a tolerance or a tolerance value. Alternatively, the position differences determined by several sensors can be combined and evaluated.

In general, reaching the tolerance (e.g. expressed as <ΔV> = <T>) can be sufficient to trigger the at least one action, or the tolerance must be exceeded (e.g. expressed as <ΔV> = <T>). Both possible conditions can be combined using the operator "≥".

It is an embodiment that a position of the at least one MR local coil measured before the start of the MR scan is established as the reference position <Vref>. The measurement of the reference position <Vref> can, for example, be carried out a maximum of 1 s to 0.1 s before the start of an MR measurement.

In one embodiment, the movement of the at least one MR local coil is determined several times during the MR scan and is compared with the specified tolerance. As a result, the movement of the MR local coil can be monitored for reaching or exceeding the permissible tolerance during the entire duration of the MR measurement will. A cycle time can for example correspond to a time interval between two MR sequences. The cycle time can be between 50 ms and 200 ms, for example, in particular around 100 ms.

One embodiment is that at least one lateral movement and / or vertical movement of the MR local coil is determined. This has the advantage that the determination of the movement can be measured particularly easily. However, the movement of the MR local coil can in principle be determined or ascertained in all three spatial directions.

It is an embodiment that the MR scan is aborted as at least one action. Additionally or alternatively, for example, a warning can be output to an operator of the associated MR system.

It is an embodiment that after the start of the method a higher tolerance is set and the method is carried out again. The selection of the higher tolerance and / or the repeated implementation of the method including the start of a new MR measurement can be carried out automatically or by an operator. If a higher tolerance is set, in particular the SAR safety factor (K-factor or VOP-factor) is adapted on the basis of the selected coil / body model so that the radiated SAR power decreases accordingly.

It is an embodiment that the tolerance is obtained from a precalculated body / coil model that provides a best approximation of a present combination of the at least one MR local coil with the associated object. For example, HF simulations can be used to determine the SAR exposure in a body for certain relative positions between the MR local coil and the patient, and from this, in turn, an associated SAR safety factor (K factor or VOP factor) for certain maximum relative movements. If the SAR safety factor is to be dimensioned in such a way that it does not reduce the output more than desired, the associated tolerance can be determined from this, which must be observed for this SAR safety factor.

For an MR measurement, a type of MR local coil used, characteristics of the patient such as body size, weight, age, gender, etc., as well as the function or position of the MR local coil on the patient (“functional classification”) can be recorded or recorded. can be determined and that advantageously precalculated HF simulation is selected therefrom, which has the best agreement (“best fit”) with the actual / real coil / body combination. The appropriate tolerance for carrying out the monitoring of a movement during the MR measurement or the MR scan is adopted from this RF simulation.

It is an embodiment that by determining the position of the at least one MR local coil, a functional classification of the at least one MR local coil (e.g. with a typical positioning on the patient for a heart coil, liver coil, etc.) is carried out and this functional classification is the best possible approximation . As a result, the functional classification no longer needs to be entered by a user, which reduces the susceptibility of the functional classification to errors and increases user-friendliness.

In one embodiment, a B0 field with a strength of at least seven Tesla is applied to the object during the MR scan. With such a field strength, the method enables a particularly high SAR performance.

It is an embodiment that at least one MR local coil has a plurality of transmitting antennas, in particular transmitting / receiving antennas, which are controlled in parallel with adjustable phase and amplitude during the MR scan. This refinement thus includes the use of the method together with the pTX method, in which the present method offers a particularly high SAR performance.

The object is also achieved by an MR system having at least one MR scanner, an MR local coil, at least one position determination device for determining a position of the at least one MR local coil and a data processing device, the data processing device being set up to perform the method as to run as described above. The MR system can be designed analogously to the method and produces the same advantages.

It is a development that the at least one position determination device comprises an optical position determination device, in particular a camera system. A position difference or movement in consecutive images can be determined by image evaluation. The MR local coil can also be provided with optical markers (e.g. reflectors, codes, light sources, etc.) in order to be able to determine the movement particularly precisely.

It is a development that the at least one position determination device comprises at least one contactless distance or proximity sensor. The distance or proximity sensor can, for example, be capacitive Proximity sensor, a laser-based proximity sensor (especially lidar), a radar sensor, an ultrasonic sensor, etc. It is a further development that at least one row with several distance or proximity sensors is present on a patient table along its length. By means of such a row, a position of the MR local coil can be determined or recognized reliably and quickly along the longitudinal extent and transversely thereto. An arrangement of two identical rows, each with several distance or proximity sensors, on both long sides of a patient table is particularly advantageous.

It is a further development that the MR local coil is an inflexible MR local coil.

The object is also achieved by a computer program product comprising commands which, when executed, cause a data processing device to execute the method as described above. The computer program product can be designed analogously to the method and results in the same advantages.

The object is also achieved by a computer-readable storage medium comprising instructions which, when executed by a data processing device, cause the data processing device to carry out the method as described above. The computer-readable storage medium can be designed analogously to the method and results in the same advantages.

• 1 zeigt in Draufsicht eine Skizze eines Patiententischs mit einem darauf liegenden Patienten und einer unflexiblen MR-Lokalspule;
• 2 zeigt ein mögliches Ablaufdiagramm des erfindungsgemäßen Verfahrens; und
• 3 zeigt ein mögliches Ablaufdiagramm einer Erweiterung des erfindungsgemäßen Verfahrens.

The properties, features and advantages of this invention described above and the manner in which they are achieved will become clearer and more clearly understandable in connection with the following schematic description of an exemplary embodiment, which is explained in more detail in connection with the drawings. For the sake of clarity, elements that are the same or have the same effect can be provided with the same reference symbols.

• 1 shows a plan view of a sketch of a patient table with a patient lying thereon and an inflexible MR local coil;
• 2 shows a possible flow chart of the method according to the invention; and
• 3 shows a possible flow chart of an extension of the method according to the invention.

1 shows a plan view of an MR system MRS with a patient table 1 and an inflexible MR local coil 2 . On the patient table 1 an object to be examined lies in the form of a human patient P .

For example, the local coil 2 be a body stem coil as shown. The local coil 2 one in relation to the patient P have a posteriorly arranged rigid part (“lower part”) and an anteriorly arranged rigid part (“upper part”), which can be movably connected to one another, for example via straps. In the top view shown, the upper part is visible.

The MR local coil 2 generally has one or more MR transmission / reception coils or antennas (not shown) that are inserted into one or more rigid parts of the MR local coil 2 are integrated. The antennas can be controlled in parallel with adjustable phase and amplitude.

The MR local coil 2 can on the patient P and / or on the patient table 1 be attached, e.g. via straps. The patient can do this P still move, which then typically also causes the MR local coil 2 is moved. The MR local coil 2 is therefore not rigid on the patient table 1 appropriate.

At the patient table 1 there is also a first position determining device 3 for determining a position of the MR local coil 2 at least in one table level of the patient table 1 , that is, a position in the longitudinal direction of the patient table 1 (x-position) and in its transverse direction (y-position). The first position determination device can do this 3 for example on both long sides of the patient table 1 one row each 3a , 3b of proximity sensors 4th have, through which both an approach of the MR local coil 2 in the y-direction as well as their displacement in the x-direction can be detected. The rows 3a , 3b of proximity sensors 4th and / or the proximity sensors 4th as such can with an evaluation device 3c the first position determining device 3 be data-technically coupled so that from the proximity sensors 4th generated measurement signals a position of the MR local coil 2 can be determined. The cycle times for successive measurements are for proximity sensors 4th very short, for example in the range of 100 ms or even shorter. In particular, measurements can also be carried out during an MR scan.

Alternatively or additionally, a second position determination device can be used 5 to determine the position of the MR local coil 2 to be available. This is an optical position determination device here 5 with a camera 5a and an evaluation device 5b for evaluating images from the camera 5a . For example, the position of the MR local coil 2 , in particular its upper part, can be determined by image evaluation. For this purpose, it is advantageous if one or more optical markers are attached to the upper part 6 are present at a previously known point. In particular, with an inclined arrangement of the camera 5a also the z-position of the MR local coil 2 and / or their inclination can be determined.

The camera 5a can be arranged on an MR device (“MR scanner”) 7 in which the patient table 1 with the patient P is retracted to record an MR scan. The MR scanner 7th can have one or more coils for the generally known generation of a B0 field, especially with a field strength of at least seven Tesla.

The camera 5a can also be used to determine a rough, “functional” position of the MR local coil before the start of an MR scan by the MR system MRS 2 relative to the patient P to determine. This can change the function or type of the MR local coil 2 , for example as a heart, abdomen, liver, etc. coil can be determined automatically, possibly also relative distances between the MR local coil 2 and the patient P . The camera 5a can do this outside of the MR scanner 7th be arranged and then in particular not be provided for the position of the MR local coil 2 to be determined during an MR scan.

The evaluation devices 3c , 5b can with a control device 8th of the MRS system MRS can be linked in terms of data technology or even at least partially functionally integrated therein. The control device 8th can be set up to do this, depending on an MR scan by the first position determining device 3 and / or second position determining device 3 specific position or movement of the MR local coil 2 to initiate at least one action, for example to cancel the MR scan. The control device 8th can also be set up in general to control the MR scan.

2 FIG. 11 shows a possible flow chart of a method for performing an MR measurement, explained by way of example using the MR system MRS from FIG 1 using only the first position determining device 3 .

In one step S1 is shortly before the start of an MR scan by means of the first position determination device 3 a reference position <Vref> of the MR local coil 2 certainly. The reference position <Vref> can have one or more position values, for example an x reference position Vref_x and a y reference position Vref_y or distance values for all proximity sensors 4th etc. In the following, it is assumed to describe the invention that the reference position <Vref> comprises the x reference position Vref_x and the y reference position Vref_y.

In one step S2 the MR scan is started. The MR scan can, for example, be carried out with a BO field with a strength of at least seven Tesla in such a way that the multiple transmit / receive antennas of the MR local coil 2 controlled in parallel with adjustable phase and amplitude during the MR scan. In particular, several spin echo trains, each with several spin echoes (so-called TSE (“Turbo Spin Echo”) method) can be generated and evaluated during an MR scan. step S2 is known in principle and is therefore not described further.

In one step S3 is used during the MR scan by means of the first position determination device 3 a new, "current" coil position <Vakt> of the MR local coil 2 determines which includes, for example, the x position Vakt_x and the y position Vakt_y.

Jedoch ist die Berechnung der Differenz nicht darauf beschränkt und kann beispielsweise gemäß $$\Delta \text{V}={\left[{\left(\text{Vakt\_x}-\text{Vref\_x}\right)}^2+{\left(\text{Vakt\_y}-\text{Vref\_y}\right)}^2\right]}^{1/2}$$

berechnet werden.In one step S4 the position difference <ΔV>, in particular in terms of amount, between the current coil position <Vakt> and the reference position <Vref> is determined, for example by <ΔV> = | <Vakt> - <Vref> | can be expressed. The position difference <ΔV> then corresponds to the movement of the MR local coil 2 . The position difference <ΔV> can be obtained, for example, by forming the difference between the individual components, for example according to $$\Delta \text{V\_x}=\left|\text{Vakt\_x}-\text{Vref\_x}\right|\text{and}\Delta \text{V\_x}=\left|\text{Vakt\_x}-\text{Vref\_x}\right|.$$

However, the calculation of the difference is not limited to this and can, for example, according to $$\Delta \text{V}={\left[{\left(\text{Vakt\_x}-\text{Vref\_x}\right)}^2+{\left(\text{Vakt\_y}-\text{Vref\_y}\right)}^2\right]}^{1/2}$$

be calculated.

It is also possible to use the respective difference values of the individual proximity sensors as the position difference <ΔV> in the y direction 4th consider. The difference in the longitudinal positions of the proximity sensors can be used as the position difference in the x direction 4th are used, the last of the series, the presence of the MR local coil 2 determine.

However, the determination of the position difference <ΔV> between the current reel position and the reference position is not limited to the above examples.

In one step S5 a comparison is made as to whether the position difference <ΔV> reaches or exceeds a specified tolerance <T>. If this is the case ("Y"), in one step S6 the MR scan aborted. If this is not the case ("N"), becomes step S3 branched back. This is carried out until in step S7 the MR scan is ended normally.

The in step S5 The comparison carried out can be carried out on a coordinate basis. For example, it can be compared whether ΔV_x T_x and / or ΔV_y T_y has occurred, T_x and T_y representing corresponding threshold values as coordinate-related components of <T>. In particular, the MR scan can be performed in step S6 canceled if only one of these conditions is met. T_x = T_y or T_x <> T_y can apply.

However, step can S6 For example, it can also be carried out if ΔV ≥ T with ΔV = [(Vakt_x - Vref_x) ² + (Vakt_y - Vref_y) ² ] ^1/2 and <T> = T a threshold value has occurred.

Alternatively or in addition, the position difference of all proximity sensors 4th be compared with a respective (possibly also the same) threshold value and step S6 be performed when the threshold for one or more proximity sensors 4th is reached or exceeded.

The tolerance <T> is specified for an MR scan and can in particular be based on the characteristic combination of the MR local coil used 2 and characteristics of the patient P be coordinated.

Optionally, after canceling the MR scan in step S6 automatically or operator-guided a higher tolerance <T> can be set and the steps S1 to S7 be carried out again. The higher tolerance <T> reduces the probability of the scan being aborted, but also the SAR performance.

3 shows a possible flow chart of an extension of the method according to the invention. This extension includes the one before the steps S1 to S7 Determination of the tolerance <T>.

Before starting the step S1 is in one step S0.1 a database with several data records is provided, which for different MR local coils 2 and specifies a respective associated tolerance <T> for patient models based on different patient data. This link between MR local coils 2 and patient models, on the one hand, and tolerances <T>, on the other hand, can for example have been determined in a basically known manner by RF calculations of various coil / body models. In a further development, the tolerance <T> can be based on a desired SAR performance or vary with a desired SAR performance.

In one step S0.2 become patient data of the patient P provided that have been previously collected.

In one step S0.3 the type / position of the MR local coil used 2 certainly. This can be done by entering appropriate data by an operator and / or by measuring. For example, the position of the MR local coil can be used before the MR scan 2 by means of a camera, for example the camera 5b , can be determined at least roughly and derived therefrom whether an abdominal coil, heart coil, etc. is present. So it can be done with the camera 5b at least one functional classification can be made

In one step S0.4 is made from the in step S0.2 provided patient data of the patient P and the one in crotch S0.3 specified and / or specific type or position of the MR local coil 2 the dataset selected that best suits the current combination of patient P and MR local coil 2 fits.

The tolerance <T> specified in the selected data record is used as the tolerance for performing the step S5 used, if necessary with the previously specified desired SAR performance.

Although the invention has been illustrated and described in more detail by means of the exemplary embodiment shown, the invention is not restricted thereto and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

In general, “a”, “one” etc. can be understood as a singular or plural number, in particular in the sense of “at least one” or “one or more” etc., as long as this is not explicitly excluded, for example by the expression “exactly a "etc.

A number can also include exactly the specified number and a customary tolerance range, as long as this is not explicitly excluded.

Claims (15)

Method (S0.1-S0.4, S1-S7) for performing an MR measurement on an object (P) by means of at least one MR local coil (2) applied to the object (P) in a relatively movable manner, in which an MR scan is carried out on the object by means of the at least one MR local coil (S2-S7), wherein - during the MR scan (S2-S7), a quantity of a movement (<ΔV>) of the at least one MR local coil (2) is determined (S3-S4) and, - if the magnitude of the movement (<ΔV>) reaches or exceeds a specified tolerance (<T>) (S5), at least one action is triggered (S6). Procedure (S0.1-S0.4, S1-S7) according to Claim 1 , in which the MR local coil (2) has at least one transmit / receive antenna and the at least one transmit / receive antenna is arranged on a rigid area of the MR local coil (2). Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which a position (<Vakt>) of the at least one MR local coil (2) and its difference are measured (S3) to determine the movement (<ΔV>) for a reference position (<Vref>) is determined. Procedure (S0.1-S0.4, S1-S7) according to Claim 3 , in which a position (S1) of the at least one MR local coil (2) measured shortly before the start of the MR scan (S2-S7) is set as the reference position (<Vref>). Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which the movement (<ΔV>) of the at least one MR local coil (2) is determined several times during the MR scan (S2-S7) and is compared with the specified tolerance (<T>). Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which at least one lateral movement (ΔV_y) and / or vertical movement (ΔV_x) of the MR local coil (2) is determined. Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which the MR scan is aborted as at least one action (S6). Procedure (S0.1-S0.4, S1-S7) according to Claim 7 , in which a higher tolerance (<T>) is set after starting the process (S6) and the process (S1-S7) is carried out again. Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which the tolerance (<T>) is obtained from a precalculated body / coil model, which is a best approximation to an existing combination of at least supplies an MR local coil (2) with the associated object (P) (S0.1-S0.4, S1-S7). Procedure (S0.1-S0.4, S1-S7) according to Claim 9 , in which a functional classification of the at least one MR local coil (2) is carried out (S0.3) by means of a position determination of the at least one MR local coil (2) and this functional classification is included in the best approximation (S0.4). Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which a BO field with a strength of at least seven Tesla is applied to the object (P) during the MR scan (S2-S7) becomes. Method (S0.1-S0.4, S1-S7) according to one of the preceding claims, in which at least one MR local coil (2) has a plurality of transmitting antennas, which during the MR scan (S2-S7) run in parallel with an adjustable phase and amplitude can be controlled. MR system (MRS), at least having an MR scanner (7), an MR local coil (2), at least one position determination device (3, 5) for determining a position (<Vref>, <Vakt>) of the at least one MR -Local coil (2) and a data processing device (3c, 5b, 8), the data processing device being set up to run the method (S0.1-S0.4, S1-S7) according to one of the preceding claims. Computer program product, comprising instructions which, when executed, cause a data processing device (8) to carry out the method (S0.1-S0.4, S1-S7) according to one of the Claims 1 to 12 execute. Computer-readable storage medium, comprising instructions which, when executed by a data processing device (8), cause them, the method (S0.1-S0.4, S1-S7) according to one of the Claims 1 to 12 execute.

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